A while back when some of you were discussing performance and fuel usage, there was mention of a speed decrease when moving into deeper water, at least that's the way I read it. If that is correct, could one or more of you explain the theory to me.

FYI on the wiper motors, if someone ever needs one, I believe they are still available from www.web4wise.com/seacure , Sea Cure Technology. They're the ones with all the Uniflite parts. I've bought window moldings, electrical parts, etc. from them and they are great to work with. If you can't find what you're looking for on their site, give Tim a call and he'll work hard at finding what you need.

Speaking of SeaCure. Right after I purchased my boat, a piling hung on the lip on one of my engine room vents, ripping it out and losing it to Davy Jones. No matter how many "sponge" dives I made, I could not find the louver, which was upsetting to say the least. I contact SeaCure and was told that they never purchased that particular mold but if I was willing to ship them one of my other vent louvers, they would make (or attempt to make) a mold and create a replacement out of plastic versus FRP, with the knowledge that it might not work in the mold too well due to the severe outter bend (or lip). Well, I took the chance on shipping one to the left coast and as it turned out, the new plastic louver worked out just great. After a couple of months in the sun, you cannot tell the difference between the ABS and FRP louvers. So, thanks to my mishap, they now have the mold for the engine vent louvers if any of you need one.

I was the guy talking about the speed increase in shallow water. It's discussed in "Basic Naval Architecture" by Barnaby on page 331 under Shallow-Water Resistance. Just whip out your Barnaby's and it will give you the explanattion of why you go faster in great detail. But I doubt many of you have Barnaby's or would want to read it without a refresher course in physics.

On a more practical note I have measured the increase in speed for my Connie as a function of decreasing depth and have it as a curve in my "Log Book of Interlude" which I carry on the bridge. Basically it says you go faster and faster as the depth decreases and that the boat performs best when running in a quarter inch of water or less. Unfortunately as depth of water drops the number of damaged props increases exponentially so you have to use a little common sense.

If you were brave enough to run in 5 feet of water you could probably pick up as much as 4 knots in speed. A great way to increase fuel economy if you can stand the cost of burned out props. For most folks though I think 10 feet is as about as shallow as one would want to cruise in. Therefore my graph stops at 10 feet.

But it's surprising. When running in deep water (greater than the length of the boat) you get two knots less than you do in water 10 feet deep. If your used to getting 18.4 knots running in shallow water (normal procedure in the Chesapeake) you feel like something is wrong with your engines when you can only get 16.4 knots in a deep spot.

If you want a copy of the graph I can mail you a copy. Don't know whether email would have the resolution or not.

Oh! I get it now. If you are in 50 ft. of water, you're pushing 50 ft. of water out of the way and if you in 10 ft. of water you are only pushing 10 ft. of water out of the way. Kinda' like a snowplow, right? Those ol' boys just fly down the road when they're pushin' 6" of snow. But let'em push 2 ft of snow and watch how slow they go! Just kiddin' Pete. That is really good info to know. I've been aware of the shallow water theory but never think to apply it when I'm in deep water and Southern Charm's only running 15 kts. I'm ready to call a diver and see what the problem is! Course' I doubt many of us will be looking very long at 18 kts this year, huh?$$?

I was getting quotes of $600+ travel and other "contingencies" to do an in place compressor replace. The cost of new was less than 2X the base quote, and it is one I can do on MY schedule...

You are correct the Marine air self contained units are pretty simple to R&R - mine had been retrofit previously with electronic thermostats, so there was no "plug & play" on dismantling control wiring. I am expecting to finish the install this weekend.

On the water depth/speed issue, after fighting the ICW last summer with 5 feet of water and 4.5 foot draft, I'll take the deep water every time ;-)

I've done business with Seacure as well for my old Uniflite, but was rather dismayed to learn the owner died about 18 months ago... the phone goes unanswered for days and the last time I needed an item (swim platform bracket), they wanted $450 + 4 weeks to fab out of an existing mold. I repaired the one I had with new 'glass matt, epoxy and paint for $30 or so...

Emory: I stopped doing 18 knots three years ago in 1985. I could see the "handwriting on the wall" and decided to go into the trawler mode. Overall, I burn about 10 gph on most of my short trips around the bay. I expect to do about 70 hours this year for a total burn of about 700 gallons. That's about two trips to the fuel dock for the year. And at $4-$5 per gallon the bill will be $2800-$3500.

I used to recommend that you keep your tanks half full on the basis that there wasn't much point in dragging around a lot of heavy fuel when you were only making short trips. Now my recommendation is to fill your tanks as full as you can as soon as you can and keep them full. The reasoning now is to buy the fuel as soon as possible before the price goes up. Of course the fuel price could go down but that seems unlikely. The brokerage yards are already overflowing with yachts for sale at bargain prices.

I sense a feeling of foreboding among yachtsmen this year. I think their not sure that they're going to be able to use their boats much this year.

BTW the shallow-water effect reverses at speeds below hull speed (about 9 knots for a Connie) so below 9 knots a Connie is more efficient in deep water.

Jim: I prefer to cruise my boat in 10'-12' of water whenever possible. Less than 10' makes me nervous. But on the Bay in poor visibility 30' is preferable because there aren't as many crab pots at that depth.

Sorry to hear that the Uniflite site may have dried up as a source of parts. We'll just have to wait and see what happens. As our boats get older we are going to have to get more adept at fixing old parts.

Your price of $600 for the new compressor seems about right. Last I heard the compressors were $350-$400 and $200-$250 certainly isn't out of line for the labor. But I think that the labor cost to put in a whole new A/C unit will be as much or more than just replacing the compressor. Hang on to the old A/C unit if you can. Its parts may be useful in repairing some of the other A/C units. Custom parts for the A/Cs can be expensive and hard to get. For example the raw water pump, which supplies water to all five A/C units, is $630 and that doesn't include the motor.

Yes, Sea Cure's a bit slow responding to e-mail and phone, however they have still been able to come through for everything I've needed help with this winter. I guess that tells the story though, during the winter we're not in a hurry to get the "stuff" for our boats. Don't give up on them yet.

Normally our boat is in the water already, but we've had an awful winter this year. We had significantly below normal snow this year, which isn't all that bad, but we also had a colder than normal winter. Without the snow cover on the ice, we were making ice all day, everyday, all winter. We hope to start launching boats this coming week. Our harbor is the most protected, so it's usually the last to see iceout. What we do though, and have been doing the last couple weeks, is opening the harbor with bubblers. By this time next week I hope to be sitting in the flybridge, feet on the stern rail, cigar and martini in hand, waiting for the HOT weather. (The only place I can have a cigar is on the boat, so it's been about 5 months.)

Ken - God bless Minnesotans but you can have it! I thought we were cold in Virginia/Maryland (guess I'm just getting old) but "open the harbor with bubblers"?? FUGGETTABOUTIT!! Hope you enjoy that cigar. You deserve it!! I have had time to even put my impellers back in yet! Of course, our typical weather is upon us.......beautiful for the last few days and rain all weekend.

I'm sitting here in my home office at 6:00 PM and the temp is 76 degrees outside. And it's sunny. I should be down working on the boat but I'm stuck here working on my taxes. I had the good fortune of getting some consulting work during the winter and therefore my tax liability went way up. The cash is great but I hate to pay the taxes. Anyway the extra cash will pay for some goodies for the boat. My wife, Arlene, has already got into the mood and spent about half of it on the house.

At the moment I don't need much Chris Craft or Uniflite "stuff". Everything seems to be working. One exception is the rub rail. I have a banged up section I would like to replace but havent been able to find it.

I'll see if I can send the speed graph as an attachment to an email. I assume you can handle .doc files.

The picture you paint of sitting on the stern with a cigar and martini is very pleasing. I don't do cigars but I can see myself sitting on the stern with a triple CC Manhattan (up) in a chilled long stem glass looking out on a golden sun going down on a flat calm Chesapeake. But hell, I haven't even stocked up the bar on the boat yet.

I guess the wife has put the kabosh on cigars at home. But don't feel bad, my neighbor's wife forces him to watch TV in thr garage (even in the freezing winter). But he doesn't feel too bad about it because he says it's the only place he can get away from the kids (he doesn't have a boat).

You folks might be familiar with Skipper Bob's cruising guides. He has written a number of them for the east coast, Intercoastal, Great Circle, etc. I saw somewhere that he has mentioned the military marina list, where veterans can sometimes get dockage, fuel, water etc. at military facilities. Have any of you taken advantage of this or have any info on it that you could share? I can't find the list or any specifics on how to use the service.

I used to follow Skipper Bob's booklets and web updates religiously but after he recently passed away I found the web site not to be well maintained. Dozier (Waterway Guide) picked it up so that may have changed. I started using cruisers.net but that doesn't cover your area.

From what I could gather, the military list is a free download but is for boats 35 to 45ft. Here is a link, you'll find the info at the bottom of the page

Thank you to those who gave input to possible easy fixes for the heat mode not working on the A/C unit. I cycled between the A/C and heat modes quite a few times and it finally kicked into giving out heat! I agree with Jim, it's nice to have an easy fix work.

Pete, I picked up about 100 feet of the aluminum rub rail channel at Jackson Marine in Northest, MD. There was still some pieces left. That was about four years ago or so (?). They had various lengths that matched the seams for the Chris, but no corner pieces. It was upstairs from the marine supply store, as I remember, in their "junk" and storage area. It was marked as for Pacemakers with the old original price. Haven't been back since. I could not find anything to match from any other source and lucked out finding it at Jackson's. I had my yard install it. The smaller trim that goes over it is still available. It was very costly to have it installed due to a mix up and confusion that I won't get into. All the pieces I bought there were used.

Hey folks - I need your help. This will be a little long, but bare with me. I went to my boat yesterday to put the impellers in and fire up, etc. Everything went smooth until I started the starboard engine. The engine fire almost immediately and with little, to no smoke. Not bad, huh? I let the engine run a few mintues and ran up the RPMS, checked the water flow and it looked ok. Got back on the boat and the engine started losing RPM and before I could reach the throttle, died. I waited a minute and started again. The engine ran for a few seconds nicely and then made a screech (at least that's what I thought I heard) and died. I went to the engine room to examine and found water spewing out of the exhaust elbow. Ok, I've got a pin hole in the elbow and it's leaking, but that won't stop and engine from running I decided to start the port engine. Good start up, little to not smoke. Went to the engine room to do a check down and discovered (yep, you guessed it) a pin hole leak in the port elbow. So I'm thinking what would shut down a diesel the way mine shut down? Severe back pressure, clogged exhaust maybe? God, I dreaded removing those elbows. But remove them I did! And WOW! The starboard elbow had leaves, twigs and a large rubber glove in it! The port elbow had two (not one, but two) aluminum beer cans in it. Now that's the engine that I've complained about, in recent posts or conversations, claiming that I was losing power on and that the exhaust note above idle speeds was softer than the starboard! But it never shut down the engine.

Question: have any of you had any type of situation like this? And what was the remedy? How did you clean out the exhaust line? I am considering renting a plumbers boroscope (they're much, much longer the any others) and having a look-see. What do you think of that idea?

This has been a pain-in-the-ass weekend. You know, bulbs that won't burn, switches that stick, etc. etc. but the removal of those elbows! Man, I feel like someone took me out in a parking lot and beat the crap out of me! But they're off and I will have the welded and repaired. I have a very good man that can do that sort of stuff.

What really gets me is the tenacity of those little critters! How the hell do the get past the baffles in the mufflers??

What a horror story! The thing that could shut your engine down is water flowing backwards from the exhaust elbow into the cylinders. If that happened at high speed it would trash your engine. At low speed it might simply make a screech and stop the engine (if you're lucky). A pinhole leak can definitely stop your engine dead in its tracks if the water has been leaking into the cylinders. To have it happen simultaneously on both engines is almost unheard of. And if there's been water in your cylinders you need the help of a professional mechanic.

Sounds like someone tried to trash your engines. The only other thing I can think of is that somehow at some time in the past the boat was low in the water and the garbage was forced into the exhaust pipes by wind and water. If this junk got into the exhaust pipes a long time ago it would definitely explain your engines poor performance. Excessive exhaust back pressure; I think I mentioned that was one of the things you should check for. But it's amazing this junk wasn't blown out of the tailpipe.

Somewhere between the exhaust elbow and the tailpipe, I believe there is a muffler and that's probably where most of the junk has hung up. The muffler may be nothing more than a couple baffle plates. I've looked into my tailpipes when the boat was in drydock and think I saw something about 4 or 5 feet up the pipe. But I'm not sure of the distance. Stick a broom handle into the tailpipe and see how far it will go. That may give you some idea of where the muffler is.

I think the last price I heard of on cast iron risers was about $500 plus installation. Figure a kilobuck per engine. If they're stainless the riser can be repaired.

Very sorry to hear of your problems and hope they aren't as serious as they appear.

That is a horror story! It sounds to me like you have or had critters nesting.

On my boat, the mufflers and entire exhaust system can be accessed by removing the plywood panels under the port and starboard drawers in the aft stateroom. Also, the panels under the head sinks and under the drawers in the den. The panels are easy to remove but separating the exhaust hoses will be more difficult, as you probably already know. Soapy water, a couple of stiff putty knives and flat screwdriver seem to work best. A heat gun may also help soften the hoses as long as you don't overdo it. Most likely, you will also find that all of the insulation is "dead" foam and will need to be replaced.

I think John's estimate of the exhaust pipe diameter is about right. I would have guessed about 10" but I haven't measured it recently.

Apparently the "critters" that John speaks of must be beer drinking critters and must also be critters who wear rubber gloves. The only critters I can think of that match that description are humans.

From your description of the debris it sounds like the kind of stuff you find floating around in the corners of every marina. The mystery is how did it get all the way up to the exhaust elbows. The exhaust outlets are normally about 2" above the water line and they rise all the way up to the elbows at which point they must be about 6" or more above the water line.

The exhaust pipes start in the engine room and run along the port and starboard sides all the way back to the transom. If they are simply open pipes it's possible that at some time the boat was partially flooded and the stuff simply floated up there. But a more likely scenario is that the stern was facing into wind driven waves which pushed the debris all the way up to the exhaust risers.

Since you have the exhaust elbows out you might be able to sluice out the debris with a high pressure fire hose from the engine end of the exhaust pipes. There are also guys who clean out the hot air ducts built into slab built houses. They might have the gear to inspect the exhaust pipes.

I think there is a muffler somewhere in the exhaust pipe. But I can't swear to that. I have never actually seen it. If there's a muffler that's a natural place for the debris to lodge and it will have to be dealt with.

John's description of the exhaust pipes is pretty much the same as mine. The pipes are about 18' long and run from the rear of the engine room to the transom. It's going to be very difficult to see if the pipes are clear without some sort of TV camera on as string. Before I tore the whole boat apart to get at the exhaust pipes I would want to see what the pipes look like. It may be possible to get a snake through the pipes and then pull some sort of cleaning bush through them to clean them out.

While you are getting ready to do that you ought to have a mechanic look at the cylinders to see there has been any damage to the engines. Of course you could also just replace the exhaust elbows, put the engine back together, cross your fingers and fire them up. But that's a risky approach. You should at least make sure the cylinders are free of water. And even then, I don't know how you could be sure there isn't still junk in the pipes that will screw up your engine's performance.

Pete, John, et al - yeah, it's a mess, but I hope it will all turn out ok. As with most of us "do-it-yourself'ers", there isn't a square inch of my boat that I do not know personally. Regarding mufflers: there are mufflers located behind the access panels in the aft cabin (and yes John, I've already had to replace the "mealy" insulation around the exhaust pipes. Nast job). The mufflers are black FRP cannisters mounted on wooden cradles and don't look like they would like to come out without some severe swearing and a half-gallon of Jim Beam. However, unlike some boats, there ARE accessible and that's a plus. Here's a couple of ideas I've come up with: 1) a small garden hoe (or rake) sized to fit inside the exhaust pipe with a handle extension. I could simply rake out the pipe from the bulkhead to the muffler and view the results. Possible?; 2) rent a plumbers boroscope and take a look-see; and another would be (and this may take place after a rake-out) attach a high pressure nozzle (similiar to Pete's firehose suggestion) to a long section of flexible pvc pipe and run down the exhaust line and see what flushes out; or lastly, a combination of all the above.

Pete- you are right about the engine and water. However, after the first involuntary shut-down. I waiting a few minutes, checked the oil appearance and help the stop button in while spining the engine (which should have spun out any water which may have intruded the cylinders) and then allowed the engine to momentarily start to lube the cylinders. Hopefully, I'm ok there, but I may pull an injector to make sure. I just hate having to do that AND deal with this exhaust thing at the same time. I'll keep everyone posted.

I cannot believe the crap that was in there. I was thinking, my boat stayed afloat during Hurricane Isabelle and Tropical Storm (whatever his name was). However, no matter how it got there, the debris is there. I am already working with a fabricator to put together a stainless screening system which will not allow any critters and/or heavy debris such as beer cans and gloves up the exhaust line.

I appreciate the advice, comments and any the ideas that the form can offer.

Agree this sounds like a mess! But I am wondering like Pete HOW the beer cans, gloves etc., got into the system to begin with? Logically it cannot get through the intake strainer, but how does this stuff (other than twigs, grass, etc) get all the way to the exhaust elbows? I've seen small birds go up exhausts to nest with the related twigs and grass, but the first time the engines are fired, it is blown out.

Who opened up the engines previously that you know about? I've found beer cans inside tires on new car and the like... I'm thinking sabotage to get more engine work from a prior mechanic?

I haven't had to winterize in the last five years but when I last did, I bought two 8" playground balls and stuffed them into the transom outlets. They were tight enough to keep out moist air and debris but probably wouldn't deter a highly motivated muskrat looking for good shelter. Most animals are opportunistic and take whatever is around them to nest, human garbage included.

Before putting the balls in place, I wrapped them with wide vinyl tape, leaving a tag that I could pull on to easily remove them in the Spring.

I like your ideas for cleaning out the exhaust tubes. You could also try a piece of PVC attached to a shop vac. Once the elbow is out, you should be able to see to the muffler, since it's a straight shot. I'm not sure about the boroscope beyond that, given the baffle angles inside the muffler.

My port side exhaust pipe puddles water inside and four years ago I found that the stainless elbow had corroded a couple of pin hole leaks. Underway, the exhaust water dripped back and made the floor in the side head wet. We were traveling, so I needed to do a quick repair in the middle of nowhere.

I used a wire wheel, emery cloth and acetone to clean the area and put generous amounts of marine tex over the holes, inside and outside the pipe. The repair is still holding. When I do need to replace the elbow, I'll probably try a fiberglass exhaust elbow. For now, I just keep an eye on it for any signs of dampness. I'm not looking forward to doing the job again.

In your case, since you will have the pipe out and are near civilization, I'd vote for replacement. Even though the pipe can be welded, new leaks can't be too far off. If you replace it, you can be pretty sure you won't need to do the job again like me.

Like Jim, my biggest question is how did all that crap get there? Sabotage by a pissed off previous mechanic? Possible, but I doubt he would sit there and feed in twigs and stuff. Beer cans and gloves would be logical though. My best guess is that it got in through the exhaust pipes but how did it get past the mufflers?

Doesn't sound like Emory wants to take out the mufflers so it doesn't seem like we'll ever know. And how long has it been there?

According to Emory, the mufflers are mounted near the transom. I thought I'd seen something back there but couldn't be sure. That means they are probably about 12' from the engine end of the exhaust pipes. And it's unlikely that the pipes are straight enough to get any sort of inflexible rod all the way down to the mufflers. At the least the pipes are going to have to be detached from the mufflers. Maybe that will be enough to clean out any crap in the mufflers themselves. If not I guess we'll have to send Emory a gallon of Jim Beam (a half gallon per engine). A visual inspection of the pipes would certainly be nice.

An 8" diameter rubber exhaust pipe is very expensive ($60 to $240 per foot depending on type) so I suspect the exhaust pipes are made in sections of something cheaper (like fiberglass) and joined together with rubber sections wherever the pipe has to go around a bend. But I don't know where the joints are except that there must be a joint where the pipe connects to the muffler. That's the key point in the exhaust system that you need to access. Cover up everything in the master stateroom because that's going to be a messy job.

I've noticed that some people install plugs in the transom end of the exhaust pipes during the winter. Now I see why. I think I'll look into something like that for my boat.

BTW, we are approaching a milestone. We are now working on page 99 and will soon transition to 100 pages on this site.

It's always advised to block off the exhaust outlets, stuffed with insulation, closed with duct tape or whatever, when storing a DD for any length of time. Being the 2 cycle types that they are, as the temps fluctuate during the fall, winter and early spring, the humid air is drawn in and out of the combustion chambers and can cause serious corrosion.

As far as making a SS screen to keep debris out, I fear they would add too much back pressure, something definitely not desireable in a DD. May I suggest rubber exhaust flappers. They flap open when the engine is started, but keep wave and wind action from letting excess water and debris in when the engine is shut down. Just my 2 cents worth.

Ken

P.S. Pete, I thought this might be the first post on page 100, but I was too quick on the draw again.

Looks like someone else will get the honors for being the first to post on the 100th page.

They used to make tapered wooden plugs to plug the exhaust pipes in the winter. Some of the older boats still use them but I don't know of a source now. Occasionally, following waves will flood the exhaust pipes on engine setups that have short exhaust pipes. That was the main purpose of the flapper valves. But the 18' exhaust pipes on Connies make that unlikely.

Whether Emory's screens would work or not depends mainly on the amount of surface area they have. If it's only a small percentage of the exhaust pipe area they would probably be all right. But I would worry that they could trap debris and cause an increase in exhaust backpressure.

The Salisbury Exhaust-Gard covers Ken has mentioned only seem to be made in relatively small sizes (3"-4" diameter). At least thats the largest I have been able to find. Also there was also one site that said Salibury had discontinued them. I haven't been able to verify that yet.

I am sorry to hear of all your problems Emory. Hope you get things sorted out soon and with not a lot of time and expense envolved. I'm with John on the risers, replace them instead of patching them. You already have them removed and if both sides are leaking it is time to replace them. As Ken did I was going to mention exhuast rubber flaps. Not sure if they could keep a critter out and how strongly they keep shut at dockside. I remember reading somewhere, before I had the Chris, that the flaps also cut down on soot build up. Doesn't seem likely. When the flaps are open they are only extending the exhaust a little and only on top. Wouldn't that be a kick if somehow they did cut down on the soot... maybe by causing the exhaust to form with the moisture?!... a guy can dream, can't he? Again I'm with Jim on those easy fixes.

Pete, let me know if you have any luck finding your rub rail. How much do you need? Was it for a small spot which you were going to piece in or were you trying to replace a section between original seems? Also you mentioned earlier that our boats should not run below 170 degrees if I remember correctly. I thought my manual states the operating temperature is 160 - 185. The reason I ask is I plan like everyone else to slow down and probably at times will want to go as slow as possible and yet maintain a proper temp, which probably means the lowest temp without causing engine problems. I may have to look into changing thermostats. I believe you said before there are two thermostats on each engine; where are they located and are they hard to check out and/or replace?

The DD Series 92 Service Manual (Sec. 5, p. 7 to 8) indicates that there are two approved thermostats for Series 92 engines. The first is a 170-187 deg F unit which is what is installed in most Connies and the second is a 180-197 deg F unit used for some special systems. I've never heard of the latter being used in a boat.

The J & T Engine Owner's Manual (Section 1: Specifications, Table 1-4, p1-8) lists the normal operating temperature range as 160-185 deg F. This temperature range is repeated in the J&T Engine Specs at the back of the manual.

So it would appear that any temp between 160 and 185 would be OK although the DD engineers would prefer that the range be limited to 170-187. Why the difference?

The difference is that 160 can be tolerated for short periods such as that necessary to idle out of the marina but is totally unacceptable for general cruising.

Nigel Clader sums it up pretty concisely on page 51 of his book Marine Diesel Engines. Nigel, by the way, has been a diesel mechanic for more than 35 years.

"The engines run cool, which causes moisture to condense in the engine. These condensates combine with sulfur to make sulfuric acid, which attacks sensitive engine surfaces. Low-load and cool running also generate far more carbon (soot) than normal, which turns diesel engine oil black after just a few hours of running. This soot gums up piston rings, and coats the valves and valve stems, leading to a loss of compression and numerous other problems."

That nasty soot which we hate so much because it dirties up our transoms is also an abrasive which scews up the innards of our engines. Soot cannot be entirely eliminated, it is a natural product of the engines operation. But it should be minimized when possible.

So if you don't mind sulphuric acid eating up the innards of your engines or the soot which sandpapers every moving part in the engine, run at the low temperature maximum soot and acid producing rpms which produce temperatures below 170 F. But if you want your engines to last a little longer try to do your cruising at engine temperatures above 170 F.

Nigel continues on page 171:

"Engines that are repeatedly operated for short periods, or are idled or run at low loads for long periods do not become hot enough to fully expand the pistons and piston rings. They then fail to seat properly and oil from the crankcase finds its way into the combustion chamber. In time the cylinders become glazed (very smooth) while the piston rings get gummed into their grooves, allowing more oil through. Oil consumption rises and compression declines. Blowby down the sides of the pistons raises the pressure in the crankcase and blows an oil mist out of the crankcase breather. Carbon builds up on the valves and valve stems and plugs the exhaust system. Valves may jam in their guides and hit pistons. Repeated short-term operattion and prolonged idling and low-load running will substantially increas maintenance costs, including major overhauls, and shorten engine life."

Again on page 221 Nigel states "Repeated running of a diesel engine at low loads is a destructive practice, which greatly increases maintenance costs and reduces engine life.

When the manuals say that 160 degrees is a normal operating temperature they mean that at a low load one should expect a temperature of 160 degrees and that a temperature of 160 does not indicate any imminent danger to the engine. But a normal temperature does not automatically mean that long term use at that temperature is good for the engine.

If it was only Nigel I would just consider that He has a "thing" against low load operation of diesels. But the same things are said by just about every author knowledgeable about diesels. The following article came from Wikopaedia:

"Engine Damage

Diesel engines can suffer damage under certain conditions that are sometimes encountered when used in a generating set- namely internal glazing and carbon buildup due to prolonged periods of running at low speeds and/or low loads. Such conditions may occur when an engine is left idling as a 'standby' generating unit, ready to run up when needed, if the engine powering the set is over-powered for the load applied to it by the alternator, or if the generator set's maximum output is far in excess of the normal loads placed on it, causing the diesel unit to be under-loaded. This is a common problem in generator sets. For example, a diesel generator set powering the lighting circuit of a building would be designed to be able to cope with the load of every light in the building being on. However, this situation rarely occurs, so for the vast majority of its operating life the diesel engine in the set will not be heavily loaded (maybe as little as 10% of the maximum load). Ideally diesel engines should run at least around 60-75% of their maximum rated load, and at around 75% of their maximum speed (although the phasing requirements of engines in generator sets can make these speeds hard to achieve).

Glazing occurs due to low combustion temperatures and pressures in the engine cylinder. When an engine is loaded correctly, the load resists the movements of the crankshaft and piston during combustion. This causes the combustion pressure to rise as the volume of the cylinder cannot increase directly in line with the increase in pressure during combustion.

Running an engine under low loads low cylinder pressures and consequent poor piston ring sealing – these rely on the gas pressure to force them against the oil film on the bores to form the seal. Low initial pressure causes poor combustion and resultant low combustion pressures and temperatures.

This poor combustion leads to soot formation and unburnt fuel residues which clogs and gums piston rings. This causes a further drop in sealing efficiency and exacerbates the initial low pressure. Glazing occurs when hot combustion gases blow past the poorly-sealing piston rings, causing the lubricating oil on the cylinder walls to 'flash burn', creating an enamel-like glaze which smooths the bore and removes the effect of the intricate pattern of honing marks machined into the bore surface.

Hard carbon also forms from poor combustion and this is highly abrasive and scrapes the honing marks on the bores leading to bore polishing, which then leads to increased oil consumption (blue smoking) and yet further loss of pressure, since the oil film trapped in the honing marks maintains the piston seal and pressures.

Un-burnt fuel leaks past the piston rings and contaminates the lubricating oil. At the same time the injectors are being clogged with soot, causing further deterioration in combustion and black smoking.

This cycle of degradation means that the engine soon becomes irreversibly damaged and may not start at all and will no longer be able to reach full power when required.

Under loaded running inevitably causes not only white smoke from unburnt fuel due to the engines failure to heat up rapidly, but over time as the engine is destroyed it is joined by the blue smoke of burnt lubricating oil leaking past the damaged piston rings, and the black smoke caused by the damaged injectors. This pollution is unacceptable to the authorities and any neighbours.

In fact at the diesels at Weymouth’s Radipole pumping station, before Wessex Water took them over and before they were converted to load management, on more than one occasion the fire brigade were erroneously called out to a supposed fire as they suffered just such an eventuality. The thick white smoke was routinely reported as a traffic hazard. Now, however, whilst housing estates have subsequently been built close up to the station there are no complaints. With a fully loaded diesel there is only a very short puff of white smoke which rapidly disappears once the diesels warm up in a matter of seconds.

Once glazing or carbon build up has occurred, it can generally only be cured by stripping down the engine and re-boring the cylinder bores, machining new honing marks and stripping, cleaning and de-coking combustion chambers, fuel injector nozzles and valves. If detected in the early stages, running an engine at maximum load and a high throttle setting for a long period, to raise the internal pressures and temperatures, might allow the piston rings to expand and scrape glaze off the bores and allow carbon buildup to be burnt off. However, if glazing has progressed to the stage where the piston rings have seized into their grooves due to glaze, this will not have any effect."

Keep in mind that a 6V92 operating at 1200 rpm is putting out less than 15% of its rated horsepower. The author above says that they should be operated at more than 60% of their rated horsepower. On a 6V92 that's about 1900 rpm.

I could go on and on but its simpler for you to just go to your favorite search engine and type in "diesels" with a qualifier of "low load running". You will get something like 68 hits many of which are other forums discussing the danger of low load running of diesels.

Even running our 6V92s at 1350 rpm which produces a temperature of about 170 F is bad for them. Going below that is extremely bad for them. We should be running them at about 1900 rpm but few of us can afford that.

I have a bent section of rub railing on the port bow. I've tried to bend it back but that's impossible. You need a long section in order to et enough purchase to bend it. I think theres a joint about 10 feet from the bow so I was looking for about a 10 foot section.

I've been doing my taxes today so I really haven't been able to call about the rub railing. And I also have a couple of priority jobs to do for my employer so it may be a day or two before I can get at it.

I think we are all running slower. I started three years ago. Unfortunately the maximum fuel economy occurs at the lowest rpms and engine temperatures. I don't think we should be greedy and push the slow running too far. We save fuel costs but we hasten the day when engine overhauls come. And with overhauls in the neighborhood of $20K to $40K per engine (depending on what's done) you have to save a lot of fuel to justify endangering your engines.

At 1400 rpm my engines run at 170 deg F and burn only 14 gph. At 70 hours per year and $4 per gallon that's $3920 per year. Suppose by going slower we can cut our fuel consumption in half (highly unlikely) so the fuel savings per year would be about $2000 per year. If an overhaul of both engines costs $40,000 (it could be much higher) it's going to take 20 years of fuel savings to pay for the overhauls. And even at the lower running speeds I don't expect to the engines will last long.

The real question is how much does low speed running shorten the lifetime of a diesel engine? This is a difficult question to answer but based on the performance of sport fishermen which do a lot of low speed running many engines fail at as little as 800 hours while a typical motorcruiser can expect about 2500 hours with good care.

No it's not that the SF engines are hopped up. I took my data from boats that had standard 6V92TIs and 6V92TAs of the same years as the Connies. The engines in the SF were the same as those in the Connies.

The difference is that a typical SF roars 80 miles out the the fishing grounds, spends 6 to 8 hours at near idle fishing and then roars back to port. The time spent at a very low load while fishing is what kills these engines.

I'm surprised that your engines are spec'd for 160 to 185 temps (same as my 6-71's). I thought you referenced 170 to 190 earlier.

I think that the Wiki article you cut and pasted is specific to diesel generators running 24/7, at speed, with little or no load. That is not the same as cruising at lower RPM where the engines are under some load. It would be more like running your engines for an extended period just to bring up the batteries, ie. the engines are running at speed but there is little or no load.

I find that my engines come up to about 165 within 20-30 minutes as long as I am above 1000 rpm and ambient air temperatures are not too cool (say above 45F). If I go on plane, the temps will rise briefly but settle back to around 165 as the thermostats adjust to the increased water flow.

Running the distances I have in the last four years and racking up about 250 hrs a year has caused me to look at my cruising habits carefully. The 2200 miles I run to Florida and back would cost me close to $20,000 if I did it on plane. At 1250 rpm, its less that $6,000 at today's fuel prices.

Worst case, that fuel savings will help pay for the inevitable re-builds but I strongly believe that more damage is done by high speed running than slow speed. We're talking about more than chump change here, so I've done a lot of reading before coming to a conclusion.

Tony Athens is a highly respected diesel tech who also administers a couple of the forums on boatdiesel.com. Here's what he says on the topic--John

Low Speed Running &"Break-In" of Marine Diesels

Seaboard MarineCustom Marine Diesel Repower Specialists

There are many perspectives and opinions floating around in the marine world that characterize low speed running or low loading of a diesel engine will adversely affect its life.. I also have my own opinions on this subject and these are based solely upon my 30 years of experience and observations in the field mixed in with some printed guidelines from Cummins Engine Company. I do have a strong opinion that with a NEW engine, break-in and operation should follow any printed guidelines from the manufacturer. In the absence of these (seems like most cases), break-in for the first few hours should consist of a mix of short time (5-15 seconds) full power use, along with at least 10-25 % of these first few hours at 70-80% of full power.. On generator applications, I recommend that 70-100% load be applied soon after start-up and the attempt be made to maintain a high load for the first 20-100 hrs of operation. The above has proven to me that if there may have been a concern about ring seating or glazing cylinder walls, that this type of use has mitigated this potential problem. The practice of using relatively high loads during break-in has also helped in finding problems with the rest of the equipment and systems on the boat..Don't forget, most new engines follow a repower or come in a new boat that have many other NEW things to, literally, "break" or "break-in"...The sooner I find these "breaks", the better for all from my perspective..

As for life expectancy on a typical modern high speed diesel engine (probably an old one too), when run at 10-50 % of its rated hp, you'll get longer life (substantially in many cases) when measured in engine hours, everything else being equal..As a general statement, Detroit diesels of WWII design built their "long life" reputation on running slow..Most of my work in the last few years has been replacing Detroit 2-strokes in commercial vessels with Cummins C series engines that are set up to run at approx 30-40% of their rated hp when cruising for long/extended periods. This WILL allow these engines to accumulate approx 20,000+ hrs of engine time before rebuild due to ring/cylinder, head and bearing wear.. The Cummins 6BT 210 is a 10,000 hr+ engine in an application that lets the engine cruise at about 50-60% of rated HP with the remainder of the hours between idle and 50% of load.. I'm also making the assumption that the engine doesn't fail due to maintenance/installation problems. I personally own a 4BT (2 cylinders less than a 6BT) that had a "top- end" at 13000 hrs and is now approaching 30,000 total hrs and still has all of the original base engine parts in it.. By far, most of its hours have accumulated at well under 50% of its rated HP.

To me, the easiest way to gage whether slow speed running is detrimental over years and years of operation is to look at commercial fishing vessels with older designed engines from Detroit, Cat, Cummins, etc... Revisiting the "Detroit" mystique again, its longevity was built on engines rated to run at 1900-2100 RPM and above, but could only last for 30+ yrs when operated continuously at 1100-1600 RPM (again, well under 50% of rated HP)..These same engines in a "crew" boat used in the off-shore oil industry, would go through "top-ends" (or worse) just about yearly when run at close to their governor settings..The longest-lived engines that I've been involved with (hrs and yrs wise), have been engines in commercial or recreational trawler type applications run at 50% of rated HP or less..Yes, there are many other parts of the equation that leads to the life of a diesel engine, but I know from experience that running them slow (i.e. cruising for days on end at hull speeds or less) is NOT a cause for concern. But some obvious things to watch out for (when running slow) are being sure your coolant temp stays up to spec. and watching for any signs of wet stacking or slobbering..Some Detroits seem to do this, but I think it's more of the general condition of that particular engine and is sometimes related to the design of the exhaust system.. A few minutes a day at higher cruise HP levels should be all that is necessary to clean things up should it be needed..

In closing, I'll mention that although this topic is brought up quite often and many people preach that you've got to use a diesel hard if you want it to last, I'm still waiting to find one that was rebuilt before its time due to low speed use..Just the opposite seems to be always the norm.

Wet stacking occurs when the engine cylinders load up with unburned fuel, especially when brought down to idle. You will notice that it smokes and may seem to run rough. This can be cleared by increasing rpms for a short period.

It's not unique to diesels. Back in the day, I had several 2 stroke dirt bikes that hated to idle. Punch the throttle a few times and they were clear. Hence the woom-bat reputation.

I know exactly what you're talking about. In one of my previous lives, I did a lot of drag racing. I built a lot of engines for myself and others. The cams we used, and I assume are still used, had a lot of overlap which caused the same situation, but I don't remember ever hearing the term. We always said it was "lumpy" gas.

Wtih the discussion of various speeds and temperatures and how they may effect engines, I was thinking of our summer slipmate Sam and his 60' Jefferson. I believe his boat has Detroit 8v92's. He mentioned to me a couple years ago or so he does not go over 8 knots. I seem to remember him saying he never runs faster to kick in the turbos even after a long run and hadn't had any problems. It never came up what temperature he runs at. He has traveled south and to the Bahamas for a few years and must have a fair amount of hours on his engines.

We spent part of the winter with Sam and coincidentally I just got an e-mail from him this a.m.

He left us in Ft. Pierce on 3/14 and went to Freeport, Nassau, Eluethra, Exumas and has just arrived at Marsh Harbor, Abacos. I've sent him an e-mail asking for details on his running, but his internet access is spotty.

He did tell me earlier that he slowed down even further on the southbound ICW trip. I'll let you know if he responds.

When you talk about WWII Detroits, remember that they were entirely different engines. A typical WWII 671 was rated at 125 hp wereas some of today's 6V71TIs are rated as high as 450 hp. I think I've even seen some rated at 475 hp. At 125 hp the cooling systems of 671s were entirely different than those that are used now on 450 hp. engines.

The 6V92TI engine is designed to run between 170 and 187 at cruising speeds and it's thermostats are designed that way. The small (only 17 degree) operating range is an indicator of the criticality of engine temperature control. That does not mean, however, that if you are idling down the channel at 1000 rpm and your temp gages read 160 F that there is anything wrong with your engines. A temp of 160 F is about normal at idle but it is not satisfactory for long term running.

I do not recommend running a diesel hard either although a short term high temp run (195 F) may burn off some some varnish and tars in the engine. It will not, however, eliminate the damage caused by low load running. Most diesels run best and last longest when run at about 60-70% of their rated horsepower which for our Connies is in the 1900-2000 rpm range.

If you want to hear about diesels failing from low load running read Nigel Calder's Marine Diesel Engines. It is available from West Marine for about $28 and should be required reading for all diesel owners. Nigel has been a diesel mechanic for over 35 years and has considerable practical experience in tearing down abused diesels. Read also David Pascoe's articles at www.yachtsurvey.com/GasDiesel.htm. And there are hundreds of other articles written by reputable authors which echo the warning about long term low load running. The 6V92 diesel must be cruised within its designed operating range of 170-187 F in order to work properly. Run over or under that range and you risk engine damage.

The bottom line for this running slow craze is the high cost of diesel fuel. Owners think they are going to save big bucks by running slow. And they will to a point. Running 700 miles @ 2000 rpm (18.4 knots & 0.48 nmpg) will burn 1,458 gallons which at $4.00 per gallon will cost you $5,832. I picked 700 miles because that is a typical yearly use. Running the same distance at 1300 rpm (10.0 knots & 0.82 nmpg) will burn only 857 gallons and cost you only $3,425 a saving of $2407 (41%). At that rpm your engines will still be running at about 170 F.

But drop down to 1200 rpm (9.2 knots & 0.94 nmpg) and your engines will still burn 757 gallons and cost you $2988 a saving of $440 more (7.5%). But they will be running at about 164 F. This is not a huge amount below 170 F but keep in mind that you really can't read or trust your temp gages to much better than 10 degrees. The engines could be running at as little as 154 F. I just don't think that running below 170 F to save $440 per year (7.5%) is worth the risk of damage to the engines.

I note that Tony Athens (the reference in John's post) says the following:

"But some obvious things to watch out for (when running slow) are being sure your coolant temp stays up to spec..."

And that's exactly what I'm worried about. Tony confirms what I'm saying. The coolant spec on 6V92s for cruising is given as 170 F and they definitely run below that at rpms below 1300.

Most of what Tony says applies to diesel generator sets not pleasure boat propuslion engines. The largest number of hours I have ever seen on a Connie (regardless of the number of overhauls) is only a little over 4000 hours and that's in 22 years (181 hours per year). Even 10,000 hours at a high end pleasure boat owner's use rate of 100 hours per year would be 100 years of use. Tony says he has an engine with 30,000 hours of use. That would be 30 years of use at pleasure boat rates. The Cummins 30BT hasn't even existed that long. He is obviously not using it as a pleasure boat engine.

BTW John, your 2200 mile trek to FL and back is going to cost you almost $10,000 ($9,361) at today's $4.00 per gallon prices and probably $12,500 at next fall's $5.00 (or more) prices. But it would be twice that much ($25,000) if you blasted down there and back at 2000 rpm.

Part of what we disagree on is probably due to the unique running characteristics of our very different engines. The in-line 6-71's that I have do not perform at the same spec's as the 6V92's that you have. My engine is an enhanced version of the WWII block that ran nearly forever until Detroit started pushing it to make more revolutions and heavier loads. Up to 485 hp on a 426 cu.in. block. Then, in the 1950's they put it in a V configuration to conserve space. Your engine is a further enhanced version of the 6V71 that was bored out to 92 cu.in. per cylinder in the late 1970's (same stroke). Up to 625 hp on a 552 cu.in. block. I'd consider that high performance, given that they started out as a naturally asprirated workhorse of 185 hp. Fortunately, neither of us have the maximum rated versions of our engines, since they are not known for their longevity.

You say that your engines need to run at 170 and can't maintain that temperature below 1300rpms. I believe you. My engines run happily at 5 to 8 degrees above minimum operating temperatures all the way down to 1000 rpms. and they never soot. However, I don't make anywhere near the speeds your engines do at various rpms. For example, at 1350, I am doing 8.5 knots, so I guess they are working harder at lower rpms (at 2400 I do 20kn). This increased load may account for why my engines stay above temperature at lower rpms. I'm confident that I'm getting good temperature readings because I check them with multiple instruments on a regular basis.

Tony Athens, Dave Pascoe and just about everyone but the manufacturers tell us that today's diesels are, by design, running on the edge at cruise speed, which is why they don't last as long as yesteryear's engines. So, as long as I can keep mine running slowly and at operating temperature, that's what I'm going to do. I'm sure I won't get 30,000 hrs but I'll bet I get more than if I ran at cruise.

As far as my Florida trips go, I've looked at the numbers very carefully. On the trip up this month I used 769 gallons over 1186 statute miles or an average of 1.54 mpg. (on legs where I didn't go on plane at all I did about 1.8 mpg). Next year, I would expect it to cost between $3,000 and $4000 each way. I can't hardly stay home that cheap.

I've mentioned this before but I would highly recommend that everyone get an engine oil analysis done, especially if your engines are sooty. As you have said, Pete, all of that soot is highly abrasive and acidic and can't be good for your engines no matter what speed you are running.

You, and I guess a lot of other Connie owners, will be glad to hear that diesel engines no longer produce soot. Now according to the EPA they produce DPM (Diesel Particulate Matter). I wonder if DPM cleans off the transom any easier than soot.

I had a pair of 300 hp. 471TIs is a previous boat (a 42' Ocean Yacht Sunliner) and they worked pretty well. In a six cylinder version they would put out 450 hp. But they had a strong tendency to overheat and I was periodically cleaning out the heat exchanger elements with muriatic acid. I don't remember what temp they ran at at low rpms.

Most pleasure boat diesels never wear out. They rot out and that occurs anywhere between 15 and 25 years with 25 being pretty optimistic. Of the major failures I've had all were rust out failures. Most of our Connies were built between 1985 and 1987 and on the average they are 22 years old now. We are going to see a lot of engine problems in the next few years.

BTW, 6V92s are not bored out versions of 671s. They are similar in design but are an entirely new engine.

At 8.5 knots a Connie has a specific resistance of about 47 lbs per ton (Froude + Wave). At 10 knots it would have a specific resistance of almost 120 lbs per ton. That's why you get good mileage. At 1350 rpm I'm doing about 10.3 knots at 170 F while you are doing 8.5 knots at 165 F. Your engines appear to be extremely lightly loaded and unless they have different thermostats than mine they are also running too cold. In order to get down to 8.5 knots most of us with 6V92s will have to drop back to about 900 rpm and at that speed the engines will definitely be way too cold. Nevertheless there will be people who will try it.

In addition to the temp and thermostat problems you must have drastically different props (or transmissions) than mine to be going 2 knots (about 20%) slower at 1350 rpm.

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